EP-A-1 540 087 discloses a wave protection structure for a slope, in this case a slope of a breakwater. At the location of a toe, the slope merges into a bed of, for example, a sea, ocean or harbour mouth. The wave protection structure is formed by wave protection elements of what are known as the interlock type. The wave protection elements which are known from EP-A-1 540 087 are provided with six projections. The projections of adjacent wave protection elements engage in one another, so that the wave protection elements together withstand the forces exerted on the individual wave protection elements by waves and current.
Wave protection elements of the known type are arranged against the slope in a more or less regular grid. Within the grid, the centres of gravity of the wave protection elements are at substantially the same horizontal grid spacing from one another. In practice, some variation in the horizontal grid spacing of individual wave protection elements is permitted without this being significantly detrimental to the overall cohesion of the wave protection structure. The individual variation with respect to the mean of the grid spacings is dependent on the type of wave protection elements and amounts to approximately 10% for the wave protection element from EP-A-1 540 087.
In practice, toe elements which are formed differently with respect to the wave protection elements are sometimes used along the toe of a wave protection structure. These toe elements ensure that the wave protection elements from the bottom row, i.e. the row which extends along the toe, under specific practical conditions remain sufficiently well in place and do not slide or tilt from the slope towards the bed. Toe elements of this type are formed, for example, from boulders, the weight of a boulder being less than the weight of a wave protection element. It is customary for the mean mass of a boulder to be ⅓ that of a wave protection element. Under extreme loads, the boulders may on average amount to 50% of the mass of the wave protection elements, in which case individual boulders, as a result of the spread in the size of the boulders, may have a mass of 60% of that of the wave protection element. The boulders are stacked on top of one another along the toe in the form of an underwater dam, in which case by way of example about seven boulders are provided in cross section. A first row of wave protection elements is provided against this underwater dam.
The known wave protection structure has the drawback that the boulders have to be positioned very carefully in order to construct a sufficiently stable underwater dam. Since work of this type in many cases takes place at a great depth and/or in cloudy water, the production of an underwater dam of this type is laborious and expensive. Another drawback is that in some cases there is only limited availability of boulders for forming an underwater dam of this type.